The present invention relates to fluid coupling devices of the type including means operable to control the quantity of fluid in the fluid operating chamber. More particularly, the present invention relates to fluid coupling devices of the type including a valve element which is actuated in response to variations in a condition sensed by a remote condition sensing device.
U.S. Pat. No. 3,055,473, assigned to the assignee of the present invention, is a typical fluid coupling device of the type well known in the prior art. The fluid coupling device includes a first rotatable coupling member defining an axis of rotation, and cover means associated with the first member to define a fluid chamber therebetween. A valve means is disposed to separate the fluid chamber into a fluid operating chamber and a fluid reservoir chamber. A second rotatable member is disposed in the fluid operating chamber and is rotatable relative to the first coupling member. The valve means is operable to control the flow of fluid between the reservoir chamber and the operating chamber and includes a valve plate defining a fluid port lying in a plane generally perpendicular to the axis of rotation. The valve means also includes a valve member disposed to move in a plane parallel to the plane of the fluid port to vary the flow area of the fluid port and the amount of fluid in the operating chamber.
Remotely actuated fluid coupling devices are especially adapted to the use of valve elements which move in an axial direction, because, in a remotely actuated coupling, movement of the valve is usually achieved by means of a device such as a solenoid or fluid pressure piston arrangement which inherently has an axial output movement.
There have been several major problems associated with axially-movable valve elements. One of the problems which has been observed in regard to axially-movable valve elements is the lack of an accurate, predictable correlation between the amount of valve lift (axial movement) and flow through the fill port. As is understood by those skilled in the art, when a flat valve arm is lifted from a port plate, the effective port area is not merely equal to the area of the port, nor is the effective port area equal to the product of the circumference of the port and the amount of lift. Instead, it has been found that because of such factors as the flow characteristics of the fluid, fluid viscosity, speed of the coupling, etc., actual valve lift must be substantially greater than the theoretical valve lift in order for the effective port area to be equal to the actual area of the port. This situation makes it even more difficult than usual to achieve a desired relationship between the external condition being sensed, such as ambient air temperature or coolant temperature, and the output speed (fan speed) of the coupling.